Rechargeable batteries, such as lithium (Li)-ion batteries, are promising candidates for various applications, including, e.g., electric vehicle applications, due to their high energy density. However, the safety of such batteries is limited due to the use of flammable liquid electrolytes. Several incidents, including a 2013 fire in the Li-ion battery unit of a Boeing 787 Dreamliner airplane, have raised questions about the safety of using Li-ion batteries for transport applications. Furthermore, the specific energy density of current state-of-the-art Li-ion batteries is below the U.S. Department of Energy Vehicle Technologies Program's long-term target for secondary batteries. Replacing flammable electrolytes and enhancing the energy density of Li-based battery technologies are at the forefront of research in both academia and industry.
Solid polymer electrolytes (SPE's) are an alternative to liquid electrolytes due to their non-volatility, low toxicity, and high energy density. SPE's can be useful in, e.g., Li-metal based batteries and related electrochemical energy storage devices that require high ionic conductivity at ambient temperature (>10-4 S/cm at 25° C.) and suppression of lithium dendrite growth. Such dendrite growth can occur in other batteries, which can cause short circuiting/over-heating/thermal run-away.
A rechargeable Li-metal based battery is considered to a promising technology for energy storage due to its high storage capacity, due to the use of lithium (Li) metal, instead of lithiated graphite. However, its use with liquid electrolytes is currently limited by the formation of irregular Li electrodeposits (dendrites) during repeated charge-discharge cycles, which often lead to short circuit causing over-heating and thermal run-away.
Many approaches have been proposed in the literature to delay dendrite nucleation, including alloying Li anodes with other metals and using additives to improve the uniformity at the solid electrolyte interface (SEI), although performance suffers due to a reduced anode capacity and durability is reduced by consumption of additives as part of the SEI films during successive charge-discharge cycles.
One group proposed that solid polymer electrolytes (SPEs) with high shear modulus (G′>6 GPa) could be used to suppress the dendrite growth. Monroe, C.; Newman, J. J Electrochem Soc 2005, 152, A396. Subsequently, another group demonstrated resistance to Li dendrite growth formation using polystyrene-b-poly(ethylene oxide) (SEO) block copolymers, thereby supporting the high modulus theory. Stone, G. M.; Mullin, S. A.; Teran, A. A.; Hallinan, D. T., Jr.; Minor, A. M.; Hexemer, A.; Balsara, N. P. J. Electrochem. Soc. 2012, 159, A222. However, while the SEO polymer showed suppressed dendrite growth at the anode, its low ionic conductivities (<10−4 S/cm at 25° C.) (Singh, M.; Odusanya, O.; Wilmes, G. M.; Eitouni, H. B.; Gomez, E. D.; Patel, A. J.; Chen, V. L.; Park, M. J.; Fragouli, P.; Iatrou, H.; Hadjichristidis, N.; Cookson, D.; Balsara, N. P. Macromolecules 2007, 40, 4578) limit its use to high temperature applications, which excludes room temperature and vehicular uses.
Thus, a need exists for an improved solid polymer electrolyte separator material that exhibits high ionic conductivity at room temperature and enhanced Li dendrite growth suppression.
While certain aspects of conventional technologies have been discussed to facilitate disclosure of the invention, Applicant in no way disclaims these technical aspects, and it is contemplated that the claimed invention may encompass one or more of the conventional technical aspects discussed herein.
In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was, at the priority date, publicly available, known to the public, part of common general knowledge, or otherwise constitutes prior art under the applicable statutory provisions; or is known to be relevant to an attempt to solve any problem with which this specification is concerned.